1. Field of Invention
The present invention relates to the field of low-voltage electrical apparatuses, and more particularly, to a control and protection device of a low-voltage electrical apparatus, where the control and protection device of a low-voltage electrical apparatus has a secondary loop connection detection device.
2. Related Art
Breakers may be used in infrequent switching of circuits and infrequent startup of motors, may be used in distribution networks to distribute electricity, may be used in the overload, short-circuit, and undervoltage protection of circuits and power supply equipments. Contactors may be used in frequently close and open circuits, and may connect, disconnect, and carrying regulated overload currents. Contactors generally have the ability of frequent operations and have long mechanical and electrical lifetime.
Control and protection of electrical equipments may be implemented by combinations of a plurality of separate devices such as breakers, contactors, thermal relays or motor protectors, and may also be implemented by a multi-functional electrical apparatus having both control and protection functions. A control and protection device consisted of a plurality of separate devices has the problem of coordination among each of the components, and is complex in installation and connection. The plurality of separate devices occupy a relatively large volume, increase costs of manufacture and usage, and are not suitable for use in limited spaces having a relatively small volume.
An electrical equipment having an device with both functions of a contactor and a breaker is disclosed in the Chinese Patent, entitled “Device Having Contactor and Breaker Functions”, and with an issue number CN1258798C. The electrical equipment has a control electromagnet and a protection device, each of which functions on moving contacts via a multi-polar device in response to manual control and electrical fault detection respectively. An electromagnet tripping device is added to a contact control mechanism. Preferably, a replaceable protection device is connected to the magnet of the relay via control circuits, and is connected to the control mechanism via tripping circuits. The power supply of the electromagnet is output to control circuits, and a tripping signal is output to the tripping circuits when a fault occurs. The electromagnet is DC type and the protection device adjusts the power supply voltage of the electromagnet. According to the solution disclosed in CN1258798C, the electromagnet tripping device is added into the contact control mechanism, the protection device is connected to the electromagnet via the control circuits and is connected to the control mechanism via the tripping circuits. Since the tripping device is outside the protection device, and the tripping device and the protection device are disposed in different modules, their electrical connection shall be conducted via external electrical connectors. Transferring signals via connectors and electrical circuits may cause decrease of reliability due to connection quality and electrical disturbance. CN1258798C also mentions, the protection device comprises a device for detecting currents flowing through a power supply conductor. To detect currents flowing through the power supply conductor, the power supply conductor must go through a detecting device, which generates a large amount of heat during usage and will greatly degrade the performance of electrical elements within the protection device and use lifetime.
A switching electrical apparatus having control and protection functions is disclosed in the Chinese Patent Application, entitled “Switching Apparatus Having Control and Protection Functions”, and with an publication number CN101494143. An AC-DC replaceable modular structure electromagnetic system is utilized, releasers, auxiliary contacts, and communication modules are respectively replaceable modules, and a plurality of auxiliary contact modules and communication modules may be selectively accessed based on users' requirements. The system not only has characteristics and functions of contactors that may be frequently operated and has long lifetime, but also has characteristics and functions of breakers that permits control, protection, and quick break. The switching electrical apparatus of this invention not only has the function of selecting releasers based on voltage type and rated current, but also has the function of voluntarily designing a turning ratio of overload and short-circuit protection, releaser grade, and number of stages of a load motor. The switching apparatus of this invention may be well-adapted, and has excellent replaceability on accessory access, requires less product types and less accessory varieties and types, has a compact overall structure, small volume, and long lifetime, greatly facilitates use and management of users, and increases adaption scope and reliability of the product. The switching apparatus having control and protection functions as mentioned in CN101494143 has a switch connected between a control power supply terminal and an electromagnet, ON/OFF status of the electromagnet is controlled by controlling the connected switch. The voltage type of the control power supply is AC voltage or DC voltage, and the voltage type of the electromagnet is selected based on the voltage type of the control power supply terminal. Or on the other hand, the voltage type of the electromagnet is AC voltage or DC voltage, and the voltage type of the control power supply terminal is selected based on the voltage type of the electromagnet. Such requirements increase restriction conditions during product usage, or increase number of varieties of products to meet usage requirements under different situations, greatly increase production and management costs, and narrow the scope of usage.
A multi-functional control and protection switching apparatus is disclosed in the Chinese Patent Application, entitled “A Multi-Functional Control and protection Switching Apparatus”, and with a publication number CN101924344. The switching electrical apparatus comprises a main circuit, a control electromagnet, a release electromagnet, and a power module of an operation mechanism. The operation mechanism controls ON/OFF status of a power supply circuit of the electromagnet by mechanically controlling a contact. The operation mechanism is mechanically correlated with a signaling contact module and a release electromagnet, and conducts the disconnection and connection of the main circuit via a transmission mechanism. The operation mechanism comprises a control and protection module and a power supply module. The control and protection module comprises a release electromagnetic drive circuit, a current sensor, and a signal processing control unit. The power supply module respectively provides power supply to the control electromagnet drive circuit, the release electromagnetic drive circuit, and the signal processing control unit. The multi-functional control and protection switching apparatus of this invention utilizes a all-in-one modular structure design to provide a switching apparatus that has control functions of a contactor, the short-circuit breaking functions of a breaker, and the overload protection functions of an overload relay. The control and protection module provided in CN101924344 comprises a release electromagnet drive circuit and a current sensor. A primary loop of the current sensor is connected to the main circuit via a clamp or a plug, and an induction signal of the secondary loop of the current sensor is connected to the signal processing control unit, so as to detect and determine the main circuit currents. Since the control and protection module comprises the current sensor, the heat generated during the usage of the current sensor may influence the usage performance and lifetime of neighboring elements. Since the primary loop of the current sensor is connected to the main circuit via a clamp or a plug, the way of connection increases resistance and temperature at the connection position. The reliability of connection will directly influence the measurement precision of the current sensor so as to influence the whole product.
A modularized multi-functional switching apparatus is disclosed in the Chinese Patent Application, entitled “A Modularized Multi-Functional Switching Apparatus”, and with a publication number CN01923988. The switching apparatus comprises: a pedestal 1, a case 2, an electromagnetic transmission mechanism 5, an operation mechanism 4, and a main circuit contact set 3. The main circuit contact set 3 is equipped with a connector terminal on its rear end, and may connect to a load via a lead or a conductive row. An inner surface on the rear end of the case 2 fits an inner surface of a rear end of the main circuit contact set 3. The switching apparatus may also comprise an auxiliary module, a thermal magnetic releaser, a digitalized controller, and an isolation mechanism. The modularized multi-functional switching apparatus utilizes a modularized structure design, selects different modules to constitute different types of products, and has a small volume. Coordination of control and protection is implemented inside the product. The product is convenient for wiring, has high reliability, saves energy and material, and has relatively high economic and social benefits. The modularized multi-functional switching apparatus disclosed in. CN101923988 utilizes a thermal magnetic releaser to implement overload protection, but has the disadvantage that the number of products increases and the production and management costs increase since protection of different scales of current grades require thermal magnetic releasers of different current scales. Further, the digitalized controller is not only required to connect to the thermal magnetic releaser, but also required to connect to a contact set terminal via screws. This way of connection makes the modular assembling indirect and inconvenient, and may also influence the reliability of connection.
The existing protection devices are all mechanical switching electrical apparatuses having contactor and breaker functions, thus the devices require a large number of switches so as to meet the requirements of different power supply voltages and currents of desired protection scope. Further, by controlling the main contact via an electromagnet, the switching electrical apparatus having contactor and breaker functions has limited scope of protection and cannot achieve high breaking ability of breakers since the electromagnet cannot meet the demands of quickly separating the main contact when functioning as a breaker.
Besides, for a current detection device disposed outside the protection module, the reliability of mutual plug-ins between its secondary loop and the protection module is related to the operating reliability of the control and protection switching apparatus and the safety of a primary loop to which it belongs. One possible situation is: the whole control and protection switching apparatus is in a closed status, but the secondary loop of the current detection device is not reliably inserted with the protection module so that the protection module cannot obtain the reaction of a current transformer to primary current. At this time, once a fault occurs in the primary loop, the protection module will not detect a short-circuit current. Therefore, it cannot send out a signal for breaking the primary loop and will cause an accident. Therefore, it is necessary to detect the connection reliability of the secondary loop of the current detection device.